The present invention relates to earth boring and, more particularly, to an earth boring machine for operating under conditions wherein one or both of the side walls are absent.
Until recently, tunneling has been accomplished mechanically using dynamite and various hand-operated tools. Recently tunnel boring machines have been developed having many advantages over conventional tunneling systems. For example, the new tunneling machines provide increased safety during the tunneling operation and faster muck removal. The tunnel boring machines eliminate the use of explosives, and the walls and back of the tunnel formed by the tunneling machine remain virtually undisturbed, requiring little or no support. Conventional tunneling machines, however, have encountered certain difficulties when attempting to bore a side drift off of the main tunnel or under other conditions wherein a normal side wall is missing.
If the tunnel does not have a full side wall on both sides of the machine, the cutterhead assembly will have a tendency to shift from the desired tunnel direction. The absence of firm ground normally used to guide the cutterhead assembly and to provide reaction for the side steering cylinders makes guidance of the tunneling machine impossible. An example of a tunnel without a full side wall is when a tunnel being bored intersects an existing tunnel, losing its side wall at the intersection. Another example is when a branch drift is bored from a main drift and the machine is subsequently backed out of the branch drift to further advance the heading of the original main drift.